A wide variety of image forming/recording devices are known. However, there are just a few methods for forming/recording images on which those devices are based. Methods for image forming basically can be divided into two parts: (1) physical principles of visualizing (there are several such methods), and (2) the manner of applying the signals, that is, methods of addressing display elements (there are a few such methods, such as scanning, multiplexed addressing, active addressing). The most widely used of these are analog addressing (scanning) and discrete (matrix x-y) addressing.
As to the methods for image recording, these are basically just a mirror image of the image forming methods and are also basically divided into scanning beam methods and matrix addressing methods. Each of the matrix methods for forming an image utilizes a row of special devices, whose constructions differ in some details but are based on the same working principle. For example, the method of x-y matrix addressing is carried out by a device having a matrix of discrete elements and row and column lines to apply signals to said elements. The scanning beam method is provided by a device having a scanning beam source, a sensitive display screen, and a focusing and deflecting system. Both of these methods may be called additive type methods, as a signal is simply applied (added) to a chosen display element of the display screen in order to activate it.
An important property in image formation is the resolution produced by a display. Sometimes the situation regarding resolution is even paradoxical. That is, computer displays, the devices most frequently used with computers, have much less resolution than other computer peripherals, such as printers, scanners, etc. It is customary to consider that the resolution of a display is primarily a technological problem. For example, in the case of matrix devices it is limited by the number of elements of the device. When dealing with a small size display, the size of whose elements is small. It also can be shown that resolution is related to the addressing technique. For example, in matrix devices that contain a large array of small size elements of less than a million such elements, such as in active matrix thin film transistor (TFT) liquid crystal displays, the technology of producing such a display and its matrix addressing circuits is complex, making the display rather expensive.
Also, there are cases where it is highly complex, or even impossible from the level of existing technology, to produce large multi-element displays, as in the case of light emitting diode (LED) displays. Furthermore, increasing the number of elements also increases the complexity of the system and consequently the probability that some of the elements might break down over time.
In the case of devices based on a scanning method, higher resolution may be obtained than can be achieved in matrix devices. Here the resolution is determined by the diameter of the scanning beam and scanning frequency. But scanning based devices generally cannot be made light-weight and flat and usually require high voltage for operation. Moreover, in devices having a cathode ray scanning beam, the electrostatic repulsion of electrons hinders reducing the beam diameter. Devices using a coherent light scanning beam also have relatively large dimensions, a small beam deflection angle, and a complex control system.
Another aspect concerning resolution comes into play while displaying (or recording) full motion video. For example, in motion pictures played back at 30 frames per second, the higher the resolution (the number of pixels), the higher must be the speed of pixel addressing. A customary way to do this is to increase the speed of applying signals (frequency increase). But this decreases the time during which a signal is applied to a pixel, which is not always compatible to improving resolution.
Apart from above cited additive type methods, a recent method for rapid addressing of display elements forms a picture using the procedure of reverse orthogonal transformation (ROT) of a data signal compressed by orthogonal transformation (OT). A compressed data signal contains many fewer signal components than a non-compressed one so fewer steps are needed to address all the display elements while the procedure of ROT is performed directly in the display elements. This is an example of a multiplication type method where the signals applied to each display element are multiplied in the element. The method comprises the procedure of inner matrix multiplication of the data signal matrix and the address signal matrix. Such a method and apparatus therefor are described in U.S. application Ser. No. 08/464,900, filed Jul. 3, 1995, assigned to the same assignee. But this method is valid only for matrix devices and though it provides an increase in the speed in presenting the image display, it requires a more complex electronic circuit scheme for an element than in, for example, an additive type TFT active matrix display, and this consequently occupies more space in the display and leads to a decrease in display device resolution.
Therefore, a need exists for a light and flat device for image forming and image recording having a simple structure, a minimized number of active elements, and that produces a resolution close to the resolution obtainable with photographic techniques.